1. Field of the Invention
The present invention relates to a mobile terminal, a mobile communication system, a base station searching method, and a storage medium which stores a base station searching program, and particularly to a technology which reduces the time required for a base station search (hereinafter, referred to as base station search time).
2. Description of Related Art
In a mobile communication system, a plurality of radio channels are applied to wireless communication between mobile terminals such as mobile phones and base stations. For example, as shown in FIG. 5, in wireless communication based on GSM (Global System for Mobile communications) method, a plurality of frequency bands composed of GSM 850 (using 850 MHz band), GSM 900 (using 900 MHz band), DCS (Digital Communication System) 1800 (using 1800 MHz band) and PCS (Personal Communication Service) 1900 (using 1900 MHz band) are used. Further, the numbers of radio channels allocated to GSM 850, GSM 900, DCS 1800 and PCS1900 are respectively “125”, “175”, “375” and “300”, so that total number of the radio channels runs to “975”.
Therefore, a general mobile terminal searches all radio channels applied to the mobile communication system for the sake of detecting a connectable base station, upon power activation or preparing for return to an in-service area. Specifically, as shown in FIG. 6, when the power is activated (step S11), the mobile terminal sequentially searches all radio channels one by one (steps S12 to S14). Then, the mobile terminal executes a connection process (timing synchronization, location registration and the like) to a base station which uses the radio channel obtained by the above-mentioned search (step S15). Note that the mobile terminal periodically executes the base station searching process shown at the above-mentioned steps S12 to S14, upon being in an out-of-service state (upon being located in an out-of-service area).
However, the above-mentioned mobile terminal has a problem that the base station search time is long, so that convenience for a user using the mobile terminal is reduced. For example, when it takes about “5 msec” for the search per channel in a mobile communication system to which the GSM method is applied, the base station search time becomes about “5 sec” (≈5 msec*975 channels).
A mobile terminal addressing this problem is disclosed in e.g. Japanese Unexamined Patent Application Publication No. 2007-116561 (Ito). This mobile terminal disclosed by Ito searches only a radio channel obtained by the previous search upon a base station search to prepare for the return to the in-service area, thereby reducing the base station search time.